Des-aspartate-angiotensin I is an endogenous angiotensin peptide (Sim and Qiu, Regul. Pept., 111:179-182 (2002)). It is formed from angiotensin I by a specific aminopeptidase present in blood vessels and the hypothalamus (Sim, Biochem. Pharmacol., 45:1524-1527 (1994); Sim et al., Biochem. Pharmacol., 48:1043-1046)). Our previous studies have shown that des-aspartate-angiotensin I exerts useful cardiovascular and renal actions (U.S. Pat. Nos. 5,773,415; 6,100,237; US2003/0086920 A1; U.S. Pat. No. 6,589,938 B2) attenuates insulin resistance in type 2 diabetic animals and combats viral infection (Sim et al., Endocrinology, 148:5925-5932 (2008); PCT No. WO 2007/030082 A1). Earlier studies have also shown that des-aspartate-angiotensin I acts as an agonist on the angiotensin AT1 receptor and that its actions were indomethacin sensitive (Sim and Soh, Eur. J. Pharmacol., 284:215-219 (1995); Sim and Chai, Br. J. Pharmacol., 117:1504-1506 (1996); Min et al., Regul Pept., 95:93-97 (2000); Wen et al., Regul Pept., 120:149-153 (2004)). The present invention identifies a specific interaction between des-aspartate-angiotensin I and the angiotensin AT1 receptor in which only prostaglandins E2 and I2 (PGE2 and PGI2) are produced by the enzymatic action of COX1. PGE2 and PGI2, so produced, mediate the biological actions of des-aspartate-angiotensin I. PGE2 acts on its receptor, which exists as four subtypes (EP1 to EP4). It produces a variety of responses which blur the line between it being categorized as a proinflammatory or anti-inflammatory molecule, (Fraser, Int. Rev. Immunol., 27:320-350 (2008)). PGE2 and PGI2 are involved in inflammation-related vasodilation and synergize with other proinflammatory mediators to increase vascular permeability and promote edema (Khanapure et al., Curr. Top. Med. Chem., 7:311-340 (2007)). Current understanding of the roles of COX1 and COX 2 in physiology, pathophysiology and inflammation are also equivocal and there are conditions where either COXs could be involved in inflammation (Rouzer and Marnett, J. Lipid Res., 50:S29-S34 (2009)). In the context of the dual pro- and anti-inflammatory roles of PGE2 and PGI2, and COX1 and COX2, this invention shows a specific novel pathway in which des-aspartate-angiotensin I acts on the angiotensin AT1 receptor and activates only COX1 to produce PGE2 and PGI2. In the setting of diseases and pathologies that are inflammatory in nature, it was surprisingly discovered that the PGE2 and PGI2 so produced attenuate the symptoms of the diseases and pathologies.
Inflammation is a complex response to injurious stimuli and is mediated and influenced by pleiotropic cytokines. Hence, an earlier study by Rufaihah et al. wrongly concluded that the cardioprotective effect of des-aspartate-angiotensin I was due to its suppression of genes of pro-inflammatory cytokines IL-6, TGF-β and GM-CSF that were upregulated in the rat model of myocardial infarction (Rufaihah et al., Life Sci., 78:1341-1351 (2006)). Firstly, the cytokines IL-6, TGF-β and GM-CSF have been shown to exhibit anti-inflammatory properties. IL-6 is an anti-inflammatory cytokine and attenuates the production of TNF-α in inflammation (Ulich et al., Am. J. Pathol., 138:1097-1101 (1991); Denis, J. Leuko. Biol., 52:197-201 (1992)). This probably accounted for the absence of des-aspartate-angiotensin I effect on upregulated TNF-α gene in the first 7 days of Rufaihah's study. TGF-β is a potent anti-inflammatory cytokine; surviving mice with knockout TGF-β gene exhibit fulminating inflammatory lesions of the heart and other organs (Kulkarni and Karlsson, Am. J. Pathol., 143:3-9 (1993)). In addition, high level of TGF-β in cow milk has been shown to protect against inflammation in mice (Ozawa et al., J. Nutr., 139:69-75 (2009)). GM-CSF is highly pleiotropic and has been shown to exhibit anti-inflammatory actions in inflammatory gut diseases (Korzenik et al., N. Engl. J. Med., 352:2193-2201 (2005); Sainathan et al., Inflamm. Bowel Dis. 14:88-99 (2008)). Secondly, cytokine gene profile in the contralateral area of normal heart tissues was also affected by des-aspartate-angiotensin I especially TNF-α gene, which increased in level in des-aspartate-angiotensin I treated animals in Day 3. Thirdly, an increase in cytokine gene expression does not necessarily translate to protein expression of the cytokine. Therefore, Rufaihah's study does not teach that the actions of des-aspartate-angiotensin I are anti-inflammatory in the rat model of myocardial infarction. It, however, teaches that des-aspartate-angiotensin I exerts cardioprotective effects, which resulted in the gradual normalization of upregulated gene expression of IL-6, TGF-β, and CM-CSF.
The ability of des-aspartate-angiotensin I to combat diseases bearing different pathologies and in different organs is not only unique but intriguing. While researching the mechanisms of its multi-disease action, it was surprisingly found that DAA-I specifically halts the early events of inflammation. These anti-inflammatory actions were useful in inflammatory diseases arising from chemical, physical, and biological insults and/or causes.